Stockholders' Equity - Earnings per Share (Details) - shares shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Equity [Abstract]
As reported shares (in shares)	1,023	1,003	1,016	998
Effect of stock-based compensation (in shares)	6	7	5	7
Diluted shares (in shares)	1,029	1,010	1,021	1,005